U.S. patent number 8,902,772 [Application Number 13/273,136] was granted by the patent office on 2014-12-02 for antenna diversity for magnetic induction radio.
This patent grant is currently assigned to NXP, B.V.. The grantee listed for this patent is Ludo Albert Lenaerts. Invention is credited to Ludo Albert Lenaerts.
United States Patent |
8,902,772 |
Lenaerts |
December 2, 2014 |
Antenna diversity for magnetic induction radio
Abstract
A magnetic induction system is disclosed, which has antenna
diversity at the transmitter side, but which does not require a
bidirectional link to pass information regarding received signal
quality back to the transmitter. The system uses a time division
multiplexing access (TDMA) arrangement, to transmit the same, or
correlated, information with a level of redundancy, from two, or
more, antenna to at least a receiver. The or each receiver is
configured to determine a received signal quality from the channel
received from one antenna, and, in response to inadequate signal
quality, to switch to another antenna. A receiver, and a
transmitter for such a magnetic induction system are also
disclosed, as is an associated method. A non-limiting application
of such a system is in binaural hearing aids, in which antenna
diversity is preferred at the transmitter because of space
limitations.
Inventors: |
Lenaerts; Ludo Albert (Hasselt,
BE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Lenaerts; Ludo Albert |
Hasselt |
N/A |
BE |
|
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Assignee: |
NXP, B.V. (Eindhoven,
NL)
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Family
ID: |
43639925 |
Appl.
No.: |
13/273,136 |
Filed: |
October 13, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120269076 A1 |
Oct 25, 2012 |
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Foreign Application Priority Data
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Oct 14, 2010 [EP] |
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10187547 |
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Current U.S.
Class: |
370/252; 455/500;
702/66; 455/504; 370/310 |
Current CPC
Class: |
H04B
5/06 (20130101); H04R 25/552 (20130101); H04B
5/0006 (20130101); H04R 25/554 (20130101); H04B
7/0615 (20130101); H01Q 21/28 (20130101); H04B
7/0608 (20130101); H04R 2225/51 (20130101) |
Current International
Class: |
H04L
1/06 (20060101) |
Field of
Search: |
;370/352 ;455/500
;702/66 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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98/44591 |
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Oct 1998 |
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WO |
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2006074655 |
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Jul 2006 |
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WO |
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WO 2011/007210 |
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Jul 2009 |
|
WO |
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Other References
Extended Search Report for Patent Appln. No. 10187547.4 (Mar. 17,
2011). cited by applicant.
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Primary Examiner: Ton; Dang
Assistant Examiner: Ambaye; Mewale
Claims
The invention claimed is:
1. A receiver for a magnetic induction transmission system
comprising: an antenna for receiving a signal having at least a
first part and a second part as a received first part and a
received second part; and a processor configured to process the
received first part and to determine a first error rate from the
received first part; the processor being further configured to, in
response to the first error rate not exceeding an error threshold,
output the processed first part without processing the second part
and without determining a second error rate from the second part,
and in response to the first error rate exceeding the error
threshold, process the received second part, determine a second
error rate from the received second part, and output the respective
one of the processed first part and the processed second part
corresponding to the lower of the first and second error rate;
wherein the signal is a time division multiple access signal, and
the first part and the second part each comprise a streaming
channel frame of a superframe of the time division multiple access
signal.
2. A receiver according to claim 1, further comprising an output
and further configured to, in response to the first error rate
exceeding both the error threshold and the second error rate, latch
the processed second part to the output.
3. A receiver according to claim 1, wherein either the first part
comprises a left channel of a time-slice of a stereophonic signal
and the second part comprises a right channel of the time-slice of
the stereophonic signal, or each of the first part and the second
part comprise the same time-slice of a monophonic signal.
4. A magnetic induction transmission system according to claim 1,
and further comprising a second receiver, the second receiver
comprising: an antenna for receiving the signal as a secondary
received first part and a secondary received second part; and a
processor configured to process the secondary received second part
and to determine a secondary second error rate from the secondary
received second part; the processor being configured to, in
response to the secondary second error rate not exceeding the error
threshold, output the processed secondary second part, and in
response to the secondary second error rate exceeding the error
threshold, process the secondary received first part, determine a
secondary first error rate from the received first part, and output
the respective one of the secondary processed first part and the
processed secondary second part corresponding to the lower of the
secondary first and secondary second error rate.
5. A magnetic induction transmission system according to claim 4,
wherein the first and second receivers comprise respectively left
and right hearing aids of a hearing aid system.
6. A method of operating a magnetic induction transmission system
having a receiver, and a transmitter comprising a plurality of
antennae, the method comprising: transmitting a first part of a
signal from the first antenna, the signal comprising the first part
and a second part; subsequently transmitting the second part of the
signal from the second antennae; receiving the first part as a
received first part and the second part as a received second part;
processing the received first part and determining a first error
rate from the received first part; outputting the processed first
part in response to the first error rate not exceeding an error
threshold without processing the received second part and without
determining a second error rate from the second part; and in
response to the first error rate exceeding the error threshold:
processing the received second part; determining a second error
rate from the received second part; and outputting the respective
one of the processed first part and the processed second part
corresponding to the lower of the first and second error rate;
wherein the signal is a time division multiple access signal, and
the first part and the second part each comprise a streaming
channel frame of a superframe of the time division multiple access
signal.
7. The method of claim 6, further comprising, in response to the
first error rate exceeding both the error threshold and the second
error rate, latching the processed second part to the output.
8. The method of claim 7, wherein the latching lasts a
predetermined number of streaming channel frames.
9. The method of claim 6, wherein the first and second error rates
are each determined as an average over a predetermined number of
streaming channel frames.
10. The method of claim 6 further comprising continuously
monitoring the first error rate if the first error rate exceeds the
error threshold and reverting to outputting the processed first
part if the first error rate drops below the error threshold.
11. The method of claim 6 further comprising periodically
monitoring the first error rate if the first error rate exceeds the
error threshold and reverting to outputting the processed first
part if the first error rate drops below the error threshold.
12. A method of operating a magnetic induction transmission system
having a receiver, the method comprising: receiving a first part of
a signal as a received first part and a second part of the signal
as a received second part; processing the received first part and
determining a first error rate from the received first part;
outputting the processed first part in response to the first error
rate not exceeding an error threshold without processing the
received second part and without determining a second error rate
from the second part; and in response to the first error rate
exceeding the error threshold, processing the received second part;
determining a second error rate from the processed second part; and
outputting the respective one of the processed first part and the
processed second part corresponding to the lower of the first and
second error rate; wherein the signal is a time division multiple
access signal, and the first part and the second part each comprise
a streaming channel frame of a superframe of the time division
multiple access signal.
13. The method of claim 12, further comprising, in response to the
first error rate exceeding both the error threshold and the second
error rate, latching the processed second part to the output.
14. The method of claim 12, wherein the latching lasts a
predetermined number of streaming channel frames.
15. The method of claim 12, wherein the first and second error
rates are each determined as an average over a predetermined number
of streaming channel frames.
16. The method of claim 12 further comprising continuously
monitoring the first error rate if the first error rate exceeds the
error threshold and reverting to outputting the processed first
part if the first error rate drops below the error threshold.
17. The method of claim 12 further comprising periodically
monitoring the first error rate if the first error rate exceeds the
error threshold and reverting to outputting the processed first
part if the first error rate drops below the error threshold.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the priority under 35 U.S.C. .sctn.119 of
European patent application no. 10187547.4, filed on Oct. 14, 2010,
the contents of which are incorporated by reference herein.
FIELD OF THE INVENTION
The present invention relates to magnetic induction transmission
systems. It further relates to receivers and transmitters for such
systems, and to a method of providing a magnetic induction
transmission.
BACKGROUND OF THE INVENTION
For short-range wireless communication, that is to say for ranges
of the order of a few centimeters up to a few meters, typically
around 10 cm to around 5 m, magnetic induction transmission is an
attractive option. Rather than relying on an aerial to transmit an
electromagnetic wave as occurs in conventional radio (which shall
also be referred to hereinafter as "RF radio") transmission, in
magnetic induction transmission, a transmitter is provided with an
antenna and propagates a magnetic field. The antenna is typically a
coil. The receiver has as an antenna a further magnetic coil. The
transmitter and receiver magnetic coils form a magnetic induction
circuit, with the interlying air acting as the core. The
arrangement is in some ways analogous to a conventional
transformer, except to that the primary and secondary coils
(transmitter and receiver antennae respectively) are not
necessarily in a geometrically fixed relationship, and instead of a
ferroelectric core between them, the core is air.
The coupling between the transmitter and receiver coils, and thus
the strength of the received signal for a fixed power transmitted
signal, depends on both the distance between the transmitter and
receiver, and their relative orientation. FIG. 1 is a radial plot,
showing the relative range 1 of a signal, against the angle between
the transmitter and receiver coils. On the abscissa (x-axis) is
shown the range when the coils are co-axial, and on the ordinate
(y-axis) is shown the range, in centimeters, when the coils are
co-planar.
From the figure is clear that there is a "null spot", close to a
45.degree. orientation between the coils. In passing, it is noted
that RF radio signals suffer from similar geometrical null spots;
however RF radio also suffers from fading, which generally
over-rules the effect of nulls in the radiation pattern for most
wireless radio applications. Fading is generally not a problem for
magnetic induction radio, since the range is relatively short.
If the receiver is situated in the null spot, the received signal
strength will be significantly weaker than elsewhere. For an
application such as hearing aid support, in which the relative
spatial arrangement between the transmitter and receiver is not
known a priori, this can be a significant problem.
It is known to solve this problem by use of a technique called
antenna diversity. Typically, antenna diversity is applied at the
receiver side: instead of relying on a single coil, the receiver
has two or more coils, arranged typically orthogonally to each
other. The receiver can then switch between the multiple antennae,
based on the quality of the received signal.
An alternative solution of relying on antenna diversity is known
where the diversity is applied at the transmitter: in situations
where there is a bidirectional link, information on the received
signal quality can be returned to the transmitter, and the
transmitter can then choose between which antenna to use, based on
the information about the received signal quality.
Neither of these the solutions are ideal: in the case of
transmitter diversity there is a requirement for a bidirectional
link, which may not always be present; in the case of receiver
antenna diversity, additional space to accommodate the multiple
coils is required in the receiver, whereas replications which are
severely space constrain, such as, for example in ear hearing aids,
the additional space may not necessarily be available.
It would therefore be desirable to provide an alternative solution
to the problem of nulls-spots, which does not suffer from the above
limitations to the same extent.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a
receiver for a magnetic induction transmission system and
comprising: an antenna for receiving a signal having at least a
first part and a second part as a received first part and a
received second part; and a processor configured to process the
received first part and to determine a first error rate from the
received first part; the processor being further configured to, in
response to the first error rate not exceeding an error threshold,
output the processed first part, and in response to the first error
rate exceeding the error threshold, process the received second
part, determine a second error rate from the received second part,
and output the respective one of the processed first part and the
processed second part corresponding to the lower of the first and
second error rate. Thereby, a magnetic induction transmission
system is enabled, which uses antenna diversity at the transmitter
side, rather than at the received side, but which does not require
a bidirectional link to pass information back to the transmitter
from the receiver.
In embodiments, the receiver further comprises an output and is
further configured to, in response to the first error rate
exceeding both the error threshold and the second error rate, latch
the processed second part to the output. Thus, the receiver may be
arranged to either revert to outputting the first part immediately,
or only after a delay (which may be, for instance 9 packets or
sub-frames) in order to limit bouncing between channels with the
associated risk of transition artefacts.
In embodiments, the signal is a time division multiple access
signal, and the first part and the second part each comprise a
streaming channel frame of a superframe of the time division
multiple access signal.
In embodiments, either the first part comprises a left channel of a
time-slice of a stereophonic signal and the second part comprises a
right channel of the time-slice of the stereophonic signal, or each
of the first part and the second part comprise the same time-slice
of a monophonic signal.
According to a second aspect of the invention, there is provided a
transmitter for a magnetic induction transmission system and
comprising a first antenna and a second antenna and configured so
as to, in operation, transmit a signal comprising first part and a
second part, the transmitter being configured to transmit the first
part from the first antenna and the second part from the second
antenna, wherein the signal is a time division multiplexing access
signal, and the first part and the second part each comprise a
streaming channel frame of a superframe of the time division
multiplexing access signal.
In embodiments, either the first part comprises a left channel of a
time-slice of a stereophonic signal and the second part comprises a
right channel of the time-slice of the stereophonic signal, or each
of the first part and the second part comprise the same time-slice
of a monophonic signal.
According to a further aspect of the invention, there is provided a
magnetic induction transmission system comprising a transmitter and
a receiver each as mentioned above.
In embodiments, the magnetic induction transmission system further
comprises a second receiver, the second receiver comprising: an
antenna for receiving the signal as a secondary received first part
and a secondary received second part; and a processor configured to
process the secondary received second part and to determine a
secondary second error rate from the secondary received second
part; the processor being configured to, in response to the
secondary second error rate not exceeding the error threshold,
output the processed secondary second part, and in response to the
secondary second error rate exceeding the error threshold, process
the secondary received first part, determine a secondary first
error rate from the received first part, and output the respective
one of the secondary processed first part and the processed
secondary second part corresponding to the lower of the secondary
first and secondary second error rate.
In embodiments the first and second receivers comprise respectively
left and right hearing aids of a stereophonic hearing aid
system.
According to a yet further aspect of the invention, there is
provided a method of operating a magnetic induction transmission
system having a receiver, and a transmitter comprising a plurality
of antennae, the method comprising: transmitting a first part of a
signal comprising first part and a second part from the first
antenna; subsequently transmitting the second part from the second
antennae; receiving the first part as a received first part and the
second part as a received second part; processing the received
first part and to determine a first error rate from the received
first part; outputting the processed first part in response to the
first error rate not exceeding an error threshold; and, in response
to the first error rate exceeding the error threshold, processing
the received second part, determining a second error rate from the
received second part, and outputting the respective one of the
processed first part and the processed second part corresponding to
the lower of the first and second error rate.
In embodiments the method further comprises, in response to the
first error rate exceeding both the error threshold and the second
error rate, latching the processed second part to the output.
In embodiments the signal is a time division multiple access
signal, the first part and the second part each comprise a
streaming channel frame of a superframe of the time division
multiple access signal, and the latching lasts a predetermined
number of streaming channel frames.
In embodiments, the first and second error rates are each
determined as an average over a predetermined number of streaming
channel frames.
These and other aspects of the invention will be apparent from, and
elucidated with reference to, the embodiments described
hereinafter.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the invention will be described, by way of example
only, with reference to the drawings, in which
FIG. 1 illustrates nulls in the signal strength at the
receiver;
FIG. 2 illustrates the magnetic induction transmission system
according to an embodiment of the invention, at FIG. 2(a) operating
in a first state; at FIG. 2(b) operating in a second state, and at
FIG. 2(c) operating in a third state;
FIG. 3 shows a super-frame data layout according to a TDMA
schedule;
FIG. 4 shows an overview of TDMA slots;
FIG. 5 shows the mapping of a TDMA structure onto logical channels
according to an embodiment of the invention; and
FIG. 6 illustrates a transmission method according to an embodiment
of the invention.
It should be noted that the Figures are diagrammatic and not drawn
to scale. Relative dimensions and proportions of parts of these
Figures have been shown exaggerated or reduced in size, for the
sake of clarity and convenience in the drawings. The same reference
signs are generally used to refer to corresponding or similar
feature in modified and different embodiments
DETAILED DESCRIPTION OF EMBODIMENTS
As already discussed, for short-range magnetic induction radio, the
signal strength at the receiver can be influenced by changing the
radiation pattern of the transmitter. This can be done for instance
by using multiple antennae, which are either physically spaced
apart or have a different orientation or both. The transmitter
transmits by means of this antenna constellation. The antennae
produce different radio patterns with different positioning of the
nulls in the signal strength pattern.
In the case that the antennae transmit the same information, the
receiver can the switch between the transmitters based on reception
quality, and still receive the information. Thus, if the first
transmitter transmits a first channel, and the information provided
on this channel is the same as that provided by the second
transmitter transmitting a second channel, then there is the level
of redundancy, and irrespective of which channel the receiver uses,
it still receive the same information. Even if the antennae do not
transmit the same information, the information may be correlated.
An example is the left and right signals of a stereophonic signal.
In normal transmission, the first antenna transmits, say, the left
signal, and the second antenna transmits the other signal (the
right signal). A receiver would normally be configured to process
only one of these signals, say the left signal as a concrete
example; however, if the received signal quality is insufficient,
the receiver may be reconfigured to process the other signal, which
is the right signal in this concrete example. Although in this case
there would still be some loss of signal (that is, in the example,
the left signal) there may be circumstances where it is preferable
to receive an adequate strength right signal rather than the
inadequate strength left signal.
FIG. 2 illustrates the magnet induction transmission system
according to an embodiment of the invention. At FIG. 2(a), the
magnetic induction transmission system is shown operating in a
first, normal, state. The system comprises the transmitter 2, which
may have associated with it signal processor 4 for producing
separate signals to each of two antennae, 6 and 8 as shown.
Processor 4 typically compresses audio samples, and arranges them
for transmission by antennae 6 and 8. First antenna 6 transmits a
first logical channel COC1. The contents of the logical channel
will be described in more detail hereinbelow. Second antenna 8
transmits a second logical channel COC2.
The system has at least a receiver, and as shown may comprise two
receivers 10 and 12 respectively. Each receiver includes an
antenna, 14 and 16 respectively, and a processor 22 and 24
respectively. Each receiver outputs an output OP1 and OP2
respectively, to an output device 18 and 20 respectively, which may
be for instance a hearing aid speaker.
As will be described in more detail hereinbelow, the two antennae 6
and 8 transmit alternatively, the first antenna 6 transmitting
information in a first logical channel, COC1, and the second
antenna 8 transmitting information in a second logical channel,
COC2.
The first logical channel COC1 may comprise the left signal of a
stereophonic signal, whereas the second logical channel COC2 may
comprise the right signal of the stereophonic signal. In other
embodiments, first and second logical channels COC1 and COC2 each
carry the whole of a monophonic signal. In this latter example,
there is complete redundancy between the channels COC1 and
COC2.
The first receiver 10 receives a received signal which includes
both COC2 and COC1. However, it normally only "listens" to the COC1
part of the received signal: the processor 22 of receiver 10
extracts the COC1 information from the appropriate time-slots of
the received signal. Processor 22 further processes the COC1
information, for instance by decompressing received audio samples.
The decompressed audio sample is output as OP1 to output device 18,
such as a hearing aid speaker.
Similarly, the second receiver 12 receives a received signal which
includes both COC2 and COC1. However, it normally only "listens" to
the COC2 part of the received signal: the processor 24 of receiver
12 extracts the COC2 information from the relevant time-slots of
the received signal. Processor 24 further processes the COC2
information, for instance by decompressing received audio samples.
The decompressed audio sample is output as OP2 to output device 20,
such as a hearing aid speaker.
With regard to first receiver 10, in addition to the decompression,
processor 22 determines an error rate PER1, as will be discussed
further hereinbelow. If the error rate PER1 exceeds a certain
threshold t1, the receiver starts to "listen" to the COC2 part of
the received signal. In this case, the processor 22 may decompress
the COC2 information, to produce a further decompressed audio
sample, and derives a second error rate PER2. (The skilled person
will appreciate that in some embodiments, in particular when the
COC1 and COC2 channel both contain the same sample of a monophonic
audio signal, such further decompression may not be necessary--for
instance, it may be possible to determine the second error rate
PER2 without having to decompress the signal.) Since the part of
the received signal comprising COC2 has been received from a
different antenna compared with the part of the received signal
comprising COC1 (that is to say, antenna 8 rather than antenna 6),
the signal strength or quality of this part of the signal may be
different to that comprising COC1. Processor 22 thus compares the
error rate PER2 with the error rate PER1. If it determines that the
second part of the signal, comprising COC2, has a higher quality
than the first part of the signal, that is to say if PER2<PER1,
processor 22 directs the decompressed signal from COC2, rather than
the decompressed signal from COC1, to output device 18 as shown in
FIG. 2(b).
As will be seen from FIG. 2(b), output device 18 associated with
first receiver 10 and output device 20 associated with second
receiver 12 now receive the same output signal OP2. In the case of
a monophonic signal, OP2 is the same as OP1, and thus there is no
loss of information; in the case of a stereophonic signal, the
situation corresponds to both left and right output devices
receiving the same (either left or right) signal of the
stereophonic signal.
In the case at least of a stereophonic signal, it is not ideal that
the same channel is received by both receivers; the receiver thus
preferably reverts back to the original situation as soon as is
practicable. In one embodiment this is achieved by processor 22
continuing to monitor both PER1 and PER2, once it has switched its
output to OP2. If either the signal quality of the first part of
the received signal improves such that the condition no longer
holds that its error rate is higher than the threshold (that is to
say, it is no longer true that PER1>t1), or the relative
qualities of the two signals change such that it is no longer true
that PER2<PER1, then the processor 22 reverts to the normal
situation, and outputs OP1 to the device 18. It will be appreciated
that it may be beneficial to introduce some hysteresis to prevent
rapid bouncing between the two states, which could be disorienting
to a user. In other embodiments, processor 22 only periodically,
rather than continuously, checks the relative signal qualities, to
determine whether the output from processor to 22 should revert to
OP1. Depending on the type of information transmits, different
modes of reverting to the original configuration may be preferred:
for instance, for a monophonic signal, it may be preferred that the
first receiver 10 switches back to OP1 immediately that the signal
quality of a single sub-frame (which may correspond to a single
packet of information), is higher in COC1; in stereophonic it may
be preferable to delay the switch back either by a fixed delay, or
until an average signal quality over a plurality of subframes, for
example 9 sub-frames, is higher for COC1 than COC2.
.times..times..times..times..times..times..times..times..times..times..ti-
mes.<.times..times..times..times. ##EQU00001##
Whilst the above discussion has focused on receiver 10, it will be
immediately apparent to the skilled person that the second
processor 24 which forms part of second receiver 12 may carry out
an analogous function with regard to the received signal. Second
processor 24 may thus switch the output of second receiver 12 to
the audio sample, corresponding to COC1, that is to say, to
OP1.
Since receivers 10 and 12 occupy different positions, it is
possible that first receiver 10 receives a better quality signal
from a second antenna 8 than from the first antenna 6 at the same
time that the second receiver 12 receives a high quality signal
from the first antenna 6 than from second antenna 8. It may thus be
the case that both receivers 10 and 12 switch their output; this
situation is shown in FIG. 2(c), which is similar to FIG. 2(a)
except that receiver 10 outputs OP2 corresponding to the second
part COC2 of the received signal, and receiver 12 outputs the
output OP1 corresponding to the first part COC1 of the received
signal. In terms of any user experience for a stereophonic
transmission to binaural hearing aids, this corresponds to the user
hearing the left channel in the right ear and the right channel in
the left ear.
As discussed above, the processor 4 in the transmitter processes
the input signal by for instance compressing audio samples, and
directing information in a first logical channel COC1 to first
antenna 6, and information in a second logical channel COC2 to
first antenna 8; the antennae then broadcast alternately. This
corresponds to a time division multiplexing access (TDMA) scenario
in its broadest sense.
The invention is not limited to any specific time division
multiplexing access (TDMA) configuration; however, FIG. 3 shows a
super-frame data layout according to an exemplary TDMA schedule. A
superframe is 1236 bits long, and at a transmission rate of 298
kbps the duration of the superframe is 4.14 ms.
The superframe is subdivided into 7 TDMA slots called subframes.
Depending on the location in the superframe, a subframe is part of
a streaming channel (SCH) 30 or a random channel (RCH) 32. There
are six streaming channels followed by one random channel. In
between each subframe there is an inter-frame gap, shown at 56 on
FIG. 4, to account for the time required for receive/transmit
(RX/TX) switching, propagation delay, and clock mismatches between
devices. Each streaming channel 30 comprises a preamble (P) 34
followed by a frame synchronization word (FS) 36, followed by a
payload, and concludes with a payload cyclic redundancy check
(PCRC) 38. The payload cyclic redundancy check is implemented by
means of a Reed-Solomon forward error detection and correction
(RS-FEC). As will be immediately apparent to the skilled person,
from this RS-FEC it is possible to determine a packet error rate
(PER) associated with the streaming channel, as mentioned above. In
other embodiments, it is possible to simply count the number of
corrected samples or sub-frames, to determine the packet error
rate. In embodiments of the invention determination of,
respectively, PER1 or PER2 is carried out by receiver processor 22
or 24 from the RS-FEC data.
Although not critical for present purposes, it is noted that the
random channel 32 has broadly the same configuration as the
streaming channel 30 (that is to say, it has a preamble followed by
a stream of synchronization word followed by a payload and payload
cyclic redundancy check). However, in the case of a random channel,
the payload is preceded by a header; this header includes a MAC
signaling 46, source network address (SRC) 48, a destination
network address (Dest) 52, and a header CLC (HCRC) 50.
The random channel is used to transmit generally short control data
messages. It is thus not used in the antenna diversity at the
transmitter: that is to say, the RCH channel is transmitted from
one or other of the antennae, based on a predetermined arrangement.
Thus, in some embodiments, the RCH channel is always transmitted
from the first antenna; in other embodiments, the channel is
transmitted alternately from the first and second antenna in
consecutive super-frames; in other embodiments, any information in
the channel is transmitted twice--first from the first antenna, and
then, in the immediately subsequent sub-frame, from the second
antenna. Such an arrangement can allow for antenna diversity for
the control data, similar to that disclosed herein for
the--typically audio--data antenna diversity. In other
circumstances, where multiple signal paths are not a problem, the
channel may be transmitted from both antennae simultaneously;
however, since transmitting from both antennae is perceived as
transmitting from one virtual antenna, this typically is not
particularly advantageous.
FIG. 4 shows the configuration of a single superframe. As already
indicated, the superframe comprises 6 signal channels (SCH.sub.1,
SCH.sub.2 . . . SCH.sub.6) followed by a random channel (RHC). Each
of the channels is followed by an interframe gap 56; the length of
each signal channel plus the interframe gap is 189 bits, whilst the
length of the random channel plus its interframe gap is 112 bits:
at a transmission rate of 298 kbps, this corresponds to a total
superframe time of 4.14 ms.
According to embodiments of the invention, and as shown in FIG. 5,
the two logical channels (which may also be called
connection-orientated channels) COC1 and COC2 are constructed from
the signal channel subframes, with alternate subframes being
allocated to opposite logical channels. Thus, SCH.sub.1, SCH.sub.3
and SCH.sub.5 are allocated to the first logical channel COC1,
whereas SCH.sub.2, SCH.sub.4 and SCH.sub.6 are allocated to the
second logical channel COC2. The random Channel 32 (RCH) associated
with each subframe is not allocated to either logical channel (it
is conventionally used for one connectionless channel). In the case
of a monophonic signal, COC1 and COC2 may carry the same
information corresponding to the same compressed audio sample; in
the case of the stereophonic signal, COC1 and COC2 may carry a
compressed version of the left signal and right signal respectively
of the audio sample.
Thus in the case of a monophonic signal, there is complete
redundancy between the logical channels COC1 and COC2; if one
channel is not available, the same information can be retrieved
from the other channel. In the case of a stereophonic signal, the
logical channels do not carry the same information but they carry
closely correlated information corresponding to the left and right
signals from the same audio sample.
Turning now to FIG. 6, this shows at FIG. 6(a) the data
transmission on the transmitter side of a magnet induction
transmission system according to embodiments of the invention, and
at FIG. 6(b), the data reception and decompression at the receiver
side (for a single receiver) of a magnetic induction transmission
system according to embodiments of the invention.
At 60 is shown the output from the transmitter processor 4, against
time on the x-axis. Above this are shown at 62 the alternating
transmissions of COC1 and COC2 by first and second antenna 6 and 8
respectively.
At the lower part of the FIG. 6(b), it is shown at 64 that the
antenna 10 of the first receiver 14 receives all of the transmitted
information (COC1 and COC2). Receiver 14 processes the information
corresponding to the first logical channel (COC1), and once the
complete packet has been received and provided that its error rate
is sufficiently low (that is to say, PER1<t1), decompresses the
information, as shown at 68, and passes it (as shown by arrow 70)
to form a part of a continuous output stream 72 on the output
device 18. If, as shown at 66a for the second timeslot of logical
channel COC1, its error rate is higher than the threshold error
rate (PER1>t1), then the receiver starts to "listen" to the
second logical channel, by processing the information in the
relevant time-slot. Provided the error rate of the second logical
channel is higher than that of the first logical channel, the
processor 22 may continue to decompress the first logical channel
information and pass it to the continuous output stream 72;
however, if the processor 22 determines that the error rate of the
second logical channel is lower than that of the first logical
channel (PER2<PER1), as shown at 66b, the processor switches and
decompresses the information on the second logical channel and
directs this to the continuous output stream 72.
As discussed above, in embodiments, it is convenient to decompress
only the logical channel information which is to be passed to the
output, since this minimizes the power consumption; however, in
other embodiments, both channels are decompressed, since this
allows simple processing and can help to avoid artifacts arising
from the transition of the output from one logical channel to the
other logical channel.
It will be appreciated that although the reception at 64, error
rate evaluation at 66, and decompression at 68 are shown as being
carried out in same timeslot, without any off-set being shown, this
is schematic only, and in any practical embodiment, there will be
some time offset, since each of the processes requires a finite
amount of time. Although in general, this offset it may not be
significant, in embodiments the audio sample is decompressed after
the full packet has been received, and the decompression itself is
spread over almost a packet time for power current shaping.
However, the time offset before the decompressed signal is passed
to form a part of the continuous output stream 72 is shown, since a
sufficient latency is required so that the decompressed information
from either logical channel (COC1 or COC2) may be used to fill the
same timeslot in the uncompressed continuous data output stream
72.
From one viewpoint, then there is disclosed herein a magnetic
induction system is disclosed, which has antenna diversity at the
transmitter side, but which does not require a bidirectional link
to pass information regarding received signal quality back to the
transmitter. The system uses a time division multiplexing access
(TDMA) arrangement, to transmit the same, or correlated,
information with a level of redundancy, from two, or more, antenna
to at least a receiver. The or each receiver is configured to
determine a received signal quality from the channel received from
one antenna, and, in response to inadequate signal quality, to
switch to another antenna. A receiver, and a transmitter for such a
magnetic induction system are also disclosed, as is an associated
method. A non-limiting application of such a system is in binaural
hearing aids, in which antenna diversity is preferred at the
transmitter because of space limitations.
From reading the present disclosure, other variations and
modifications will be apparent to the skilled person. Such
variations and modifications may involve equivalent and other
features which are already known in the art of magnetic induction
transmission, and which may be used instead of, or in addition to,
features already described herein.
Although the appended claims are directed to particular
combinations of features, it should be understood that the scope of
the disclosure of the present invention also includes any novel
feature or any novel combination of features disclosed herein
either explicitly or implicitly or any generalisation thereof,
whether or not it relates to the same invention as presently
claimed in any claim and whether or not it mitigates any or all of
the same technical problems as does the present invention.
Features which are described in the context of separate embodiments
may also be provided in combination in a single embodiment.
Conversely, various features which are, for brevity, described in
the context of a single embodiment, may also be provided separately
or in any suitable sub-combination.
The applicant hereby gives notice that new claims may be formulated
to such features and/or combinations of such features during the
prosecution of the present application or of any further
application derived therefrom.
For the sake of completeness it is also stated that the term
"comprising" does not exclude other elements or steps, the term "a"
or "an" does not exclude a plurality, a single processor or other
unit may fulfill the functions of several means recited in the
claims and reference signs in the claims shall not be construed as
limiting the scope of the claims.
* * * * *